Dual metal-insulator-semiconductor contact structure and formulation method

ABSTRACT

A method of making a semiconductor device includes forming a first source/drain trench and a second source/drain trench over a first and second source/drain region, respectively; forming a first silicon dioxide layer in the first source/drain trench and a second silicon dioxide layer in the second source/drain trench; forming a first source/drain contact over the first source/drain region, the first source/drain contact including a first tri-layer contact disposed between the first silicon dioxide layer and a first conductive material; and forming a second source/drain contact over the second source/drain region, the second source/drain contact including a second tri-layer contact disposed between the second silicon dioxide layer and a second conductive material; wherein the first tri-layer contact includes a first metal oxide layer in contact with the first silicon dioxide layer, and the second tri-layer contact includes a second metal oxide layer in contact with the second silicon dioxide layer.

BACKGROUND

The present invention relates to metal-oxide-semiconductor field-effecttransistors (MOSFET), and more specifically, to source/drain contactstructures in MOSFET devices.

The MOSFET is a transistor used for switching electronic signals. TheMOSFET has a source, a drain, and a metal oxide gate electrode. Themetal gate is electrically insulated from the main semiconductorn-channel or p-channel by a thin layer of insulating material, forexample, silicon dioxide or high dielectric constant (high-k)dielectrics, which makes the input resistance of the MOSFET relativelyhigh. The gate voltage controls whether the path from drain to source isan open circuit (“off”) or a resistive path (“on”).

N-type field effect transistors (NFET) and p-type field effecttransistors (PFET) are two types of complementary MOSFETs. The NFET useselectrons as the current carriers and with n-doped source and drainjunctions. The PFET uses holes as the current carriers and with p-dopedsource and drain junctions.

SUMMARY

According to an embodiment, a method of making a semiconductor deviceincludes forming a first source/drain trench over a first source/drainregion in a first transistor and a second source/drain trench over asecond source/drain region in a second transistor; forming a firstsilicon dioxide layer in the first source/drain trench and a secondsilicon dioxide layer in the second source/drain trench; forming a firstsource/drain contact over the first source/drain region, the firstsource/drain contact including a first tri-layer contact disposedbetween the first silicon dioxide layer and a first conductive material;and forming a second source/drain contact over the second source/drainregion, the second source/drain contact including a second tri-layercontact disposed between the second silicon dioxide layer and a secondconductive material; wherein the first tri-layer contact includes afirst metal oxide layer in contact with the first silicon dioxide layer,and the second tri-layer contact includes a second metal oxide layer incontact with the second silicon dioxide layer.

According to another embodiment, a method of making a semiconductordevice includes forming a first source/drain trench over a firstsource/drain region in a first transistor and a second source/draintrench over a second source/drain region in a second transistor; forminga first silicon dioxide layer in the first source/drain trench and asecond silicon dioxide layer in the second source/drain trench;disposing a first metal oxide layer onto the first silicon dioxide layerand along a first sidewall of the first source/drain trench and over thesecond silicon dioxide layer and along a sidewall of the secondsource/drain trench; removing the first metal oxide layer from thesecond source/drain trench; disposing a second metal oxide layerfollowed by a conductive liner layer over the first metal oxide layerwithin the first source/drain trench and directly onto the secondsilicon dioxide layer and along the sidewall of the second source/draintrench; removing by a selective process, the second metal oxide layerand the conductive liner layer from the first source/drain trench; andfilling the first source/drain trench and the second source/drain trenchwith a conductive material.

Yet, according to another embodiment, a semiconductor device includes afirst transistor comprising a first substrate, a first source/drainregion positioned over the first substrate, and a first source/draincontact defined over the first source drain region, the firstsource/drain contact including a first tri-layer contact disposedbetween a first silicon dioxide layer disposed directly over the firstsource/drain region and a first conductive material; and a secondtransistor including a second substrate, a second source/drain regionpositioned over the second substrate, and a second source/drain contactdefined over the second source drain region, the second source/draincontact including a second tri-layer contact disposed between a secondsilicon dioxide layer disposed directly over the second source/drainregion and a second conductive material; wherein the first tri-layercontact including a first metal oxide layer in contact with the firstsilicon dioxide layer, and the second tri-layer contact includes asecond metal oxide layer in contact with the second silicon dioxidelayer.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIGS. 1-9B illustrate exemplary methods of making semiconductor devicesaccording to various embodiments, in which:

FIG. 1 is a cross-sectional side view of a first transistor and a secondtransistor with a silicon dioxide layer and first liner layer disposedwithin source/drain trenches;

FIG. 2 is a cross-sectional side view after disposing a mask over thesecond transistor and removing the first liner layer from the firsttransistor;

FIG. 3 is a cross-sectional side view after removing the mask anddisposing a first metal oxide layer within the source/drain trenches;

FIG. 4 is a cross-sectional side view after disposing a second linerlayer over the metal oxide layer;

FIG. 5 is a cross-sectional side view after disposing a mask over thefirst transistor and removing the first liner layer, first metal oxidelayer, and the second liner layer from the second transistor;

FIG. 6 is a cross-sectional side view after removing the mask anddisposing a second metal oxide layer and a second liner layer within thesource/drain trenches of the first and second transistors;

FIG. 7 is a cross-sectional side view after disposing a mask over thesecond transistor and selectively removing the second metal oxide layerand second liner layer from the first transistor;

FIG. 8A is a cross-sectional side view after filling with source/draintrenches of the first and second transistors with a metal according to afirst embodiment;

FIG. 8B is a cross-sectional side view after performing a planarizationprocess;

FIG. 9A is a cross-sectional side view after removing the first linerlayer from the first and second transistors and filling the source/draintrenches with a metal according to a second embodiment; and

FIG. 9B is a cross-sectional side view after performing a planarizationprocess.

DETAILED DESCRIPTION

As the dimensions of semiconductor devices scale down, the contact areaof the device source/drain regions decrease. The smaller contact areasmay result in increased resistance. Metal silicide materials may be usedto form source/drain contacts. However, depending on the type ofsubstrate, forming a metal silicide may be challenging.

Accordingly, various embodiments described herein include semiconductordevices with two transistors having different source/drain contacts thatprovide reduced contact resistance. The different source/drain contactsin the two transistors are formed simultaneously. Like referencenumerals refer to like elements across different embodiments.

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

As used herein, the articles “a” and “an” preceding an element orcomponent are intended to be nonrestrictive regarding the number ofinstances (i.e. occurrences) of the element or component. Therefore, “a”or “an” should be read to include one or at least one, and the singularword form of the element or component also includes the plural unlessthe number is obviously meant to be singular.

As used herein, the terms “invention” or “present invention” arenon-limiting terms and not intended to refer to any single aspect of theparticular invention but encompass all possible aspects as described inthe specification and the claims.

As used herein, the term “about” modifying the quantity of aningredient, component, or reactant of the invention employed refers tovariation in the numerical quantity that can occur, for example, throughtypical measuring and liquid handling procedures used for makingconcentrates or solutions. Furthermore, variation can occur frominadvertent error in measuring procedures, differences in themanufacture, source, or purity of the ingredients employed to make thecompositions or carry out the methods, and the like. In one aspect, theterm “about” means within 10% of the reported numerical value. Inanother aspect, the term “about” means within 5% of the reportednumerical value. Yet, in another aspect, the term “about” means within10, 9, 8, 7, 6, 5, 4, 3, 2, or 1% of the reported numerical value.

Turning now to the Figures, FIGS. 1-9B illustrate exemplary methods ofmaking semiconductor devices according to various embodiments. FIG. 1 isa cross-sectional side view of a first transistor 101 and a secondtransistor 102. The first transistor 101 and the second transistor 102are different transistors. In one embodiment, the first transistor 101is a PFET, and the second transistor 102 is an NFET. The firsttransistor 101 and the second transistor may be FinFET devices, planartransistor devices, or any other type of semiconductor devices.

The first transistor 101 and the second transistor 102 include asubstrate 103. The substrate 103 of the first transistor 101 can be thesame or different than the substrate 103 of the second transistor 102.Non-limiting examples of suitable substrate 103 materials includesilicon, silicon germanium, or other suitable substrate material.

The substrate 103 may be doped with an n-type dopant or a p-type dopant,depending on the type of transistor, to form source/drain regions.Non-limiting examples of suitable n-type dopants include phosphorus andarsenic. Non-limiting examples of suitable p-type dopants include boronand gallium.

In one embodiment, the first transistor 101 is a PFET, and the substrate103 includes silicon germanium doped with boron. In another embodiment,the second transistor 102 is an NEFT, and the substrate 103 includessilicon doped with phosphorus.

An interlayer dielectric (ILD) layer 110 is disposed over the substrate103 and patterned to form source/drain trenches 140. The ILD layer 110may be formed from, for example, a low-k dielectric oxide, including butnot limited to, silicon dioxide, spin-on-glass, a flowable oxide, a highdensity plasma oxide, borophosphosilicate glass (BPSG), or anycombination thereof. The ILD layer 140 is deposited by a suitabledeposition process, including, but not limited to chemical vapordeposition (CVD), physical vapor deposition (PVD), plasma enhanced CVD,atomic layer deposition (ALD), evaporation, chemical solutiondeposition, or other like processes.

To pattern the ILD layer 110, a resist, for example, a photoresist (notshown) is disposed over the ILD layer 110. The ILD layer 110 may also bepatterned using any suitable lithography process. When the resist is aphotoresist, the resist is patterned by exposure to a desired pattern ofradiation. The exposed photoresist is developed with a resist developerto provide a patterned photoresist over the ILD layer 110. At least oneetching process is employed to transfer the pattern from the patternedphotoresist into ILD layer 110. The etching process may be a dry etchprocess (e.g., reactive ion etching (RIE), plasma etching, ion beametching, or laser ablation). The etching process may be a wet chemicaletch (e.g., with potassium hydroxide or sulfuric acid and hydrogenperoxide). Both dry etching and wet chemical etching processes may beused. After transferring the pattern through the ILD layer 110 to formthe source/drain trenches 140, the patterned photoresist is removedutilizing resist stripping processes, for example, ashing. A firstsource/drain trench 140 is formed within the first source/drain trench140 of the first transistor 101. A second source/drain trench 140 isformed within the second source/drain trench 140 of the secondtransistor 102.

A silicon dioxide layer 120 is formed within the source/drain trenches140 and over the source/drain regions within the substrate 103. Thesilicon dioxide layer 120 may be formed using a chemical oxidationprocess. The silicon dioxide layer 120 is formed by an ex situ or an insitu oxidation process. During ex situ oxidation, an aqueous chemicaloxidation process forms the silicon dioxide layer 120. During in situoxidation, the source/drain trench 140 is exposed to an oxidant, such asozone, before depositing a high-k dielectric material.

The thickness of the silicon dioxide layer 120 generally varies and isnot intended to be limited. In one aspect, the thickness of the silicondioxide layer 120 is in a range from about 0.1 nm to about 1.5 nm. Inanother aspect, the thickness of the silicon dioxide layer 120 is in arange from about 0.3 nm to about 0.8 nm.

A first liner layer 130 is disposed as a conformal layer within thesource/drain trenches 140. The first liner layer 130 is disposeddirectly over the silicon dioxide layer 120, along a sidewall of thesource/drain trenches 140 within the first transistor 101 and the secondtransistor 102, and over the ILD layer 110. In some embodiments, thefirst liner layer 130 is optional.

The first liner layer 130 may include a low contact resistance materialor other suitable conductive liner material. Non-limiting examples ofsuitable materials for the first liner 130 include titanium nitride,tantalum nitride, tungsten, or any combination thereof. The first linerlayer 130 may be formed as a single layer or multi layers of one or morematerials.

The first liner layer 130 is formed using any suitable depositionprocess. Non-limiting examples of suitable deposition methods forforming the first liner layer 130 include CVD, PVD, ALD, or othersuitable deposition process.

The thickness of the first liner layer 130 generally varies and is notintended to be limited. In one aspect, the thickness of the first linerlayer 130 is in a range from about 0.5 nm to about 5.0 nm. In anotheraspect, the thickness of the first liner layer 130 is in a range fromabout 1.0 nm to about 3.0 nm.

FIG. 2 is a cross-sectional side view after disposing a mask 201 (firstmask) over the second transistor 102 and removing the first liner layer130 from the first transistor 101. The mask 201 may be any suitable etchblock mask material, for example, a resist. The mask 201 protects thesecond transistor 102 and is disposed as a conformal layer within thesource/drain trench 140 of the second transistor 102. The mask 201 isformed over the first liner layer 130. Suitable materials for the mask201 include photoresist materials, electron-beam resist materials,ion-beam resist materials, X-ray resist materials, and etchant resistmaterials. The mask 201 material may include a polymeric material thatis formed by a spin-on process.

The first liner layer 130 is removed from the source/drain trench 140 ofthe first transistor 101 by an etching process. After removing the firstliner layer 130, the silicon dioxide layer 120 is exposed in the firsttransistor 101. The etching process may include, for example, NH₄OH,H₂O₂, and H₂O, from room temperature up to 70° C.

FIG. 3 is a cross-sectional side view after removing the mask 201 anddisposing a first metal oxide layer 301 within the source/drain trenches140 of the first transistor 101 and the second transistor 102. The firstmetal oxide layer 301 may be formed by an ALD technique. The first metaloxide layer 301 is deposited as a conformal layer within thesource/drain trenches 140. In the first transistor 101, the first metaloxide layer 301 is disposed directly onto the silicon dioxide layer 120and along a sidewall of the source/drain trench. In the secondtransistor 102, the first metal oxide layer 301 is disposed directlyonto the first liner layer 130 and over the silicon dioxide layer 120.

To form the first metal oxide layer 301 by ALD, a metal precursor isflowed alternately with an oxidant, for example, O₂, O₃, or water.Suitable precursors and temperatures for thermal ALD are known in theart and can be used.

The type of metal oxide used for the first metal oxide layer 301 dependson the type of transistor. When the first transistor 101 is a PFET, thefirst metal oxide layer 301 may be aluminum oxide (Al₂O₃), titaniumoxide (TiO₂), germanium oxide (GeO₂), or any combination thereof. Whenthe first transistor 101 is an NFET, the first metal oxide layer 301 maybe yttrium oxide (Y₂O₃), lutetium oxide (Lu₂O₃), lanthanum oxide(La₂O₃), strontium oxide (SrO), zirconium oxide (ZrO₂), hafnium oxide(HfO₂), magnesium oxide (MgO), or any combination thereof.

The first metal oxide layer 301 has a thickness in a range from about0.1 nm to about 2.0 nm. In another aspect, the first metal oxide layer301 has a thickness in a range from about 0.3 nm to about 0.8 nm.

FIG. 4 is a cross-sectional side view after disposing a second linerlayer 401 over the first metal oxide layer 301. The second liner layer401 is disposed as a conformal layer over the first metal oxide layer301 within the source/drain trenches 140 of the first and secondtransistors 101, 102. The second liner layer 130 may include a lowcontact resistance material or other suitable conductive liner material.Non-limiting examples of suitable materials for the second liner layer401 include titanium nitride, tantalum nitride, tungsten, or anycombination thereof. The second liner layer 401 may be formed as asingle layer or multi layers of one or more materials. In someembodiments, the second liner layer 401 is optional.

The second liner layer 401 is formed using any suitable depositionprocess. Non-limiting examples of suitable deposition methods forforming the first liner layer 130 include CVD, PVD, ALD, or anycombination thereof.

The thickness of the second liner layer 401 generally varies and is notintended to be limited. In one aspect, the thickness of the second linerlayer 401 is in a range from about 0.5 nm to about 5.0 nm. In anotheraspect, the thickness of the second liner layer 401 is in a range fromabout 1.0 nm to about 3.0 nm.

FIG. 5 is a cross-sectional side view after disposing a second mask (notshown) over the first transistor 101 and removing the first liner layer130, the first metal oxide layer 301, and the second liner layer 401from the source/drain trenches 140 of the second transistor 102. Anystandard or suitable block mask and lithography processes may be usedfor the second mask. The first liner layer 130, the first metal oxidelayer 301, and the second liner layer 401 are removed by an etchingprocess. The etching process may include a three step process, forexample, (1) a process that includes NH₄OH, H₂O₂, and H₂O, (2) a processthat include dilute HF:H₂O (1:100 to 1:500), and (3) a process thatincludes NH₄OH, H₂O₂, and H₂O.

After removing the first liner layer 130, the first metal oxide layer301, and the second liner layer 401 from the second transistor 102, thesilicon dioxide layer 120 is exposed. The first metal oxide layer 301and the second liner layer 401 remain within the source/drain trenches140 of the first transistor 101.

FIG. 6 is a cross-sectional side view after disposing a second metaloxide layer 601 and a third liner layer 602 within the source/draintrenches 140 of the first and second transistors 101, 102. The secondmetal oxide layer 601 may be formed by an ALD technique. The secondmetal oxide layer 601 is deposited as a conformal layer within thesource/drain trenches 140. The second metal oxide layer 601 is disposeddirectly onto the second liner layer 401 within the source/drain trench140 of the first transistor. The second metal oxide layer 601 isdisposed directly onto the silicon dioxide layer 120, along a sidewallof the source/drain trench, and over the ILD layer 110 of the secondtransistor 102.

The type of metal oxide used for the second metal oxide layer 601depends on the type of transistor. When the second transistor 102 is aPFET, the second metal oxide layer 601 may be aluminum oxide (Al₂O₃),titanium oxide (TiO₂), germanium oxide (GeO₂), or any combinationthereof. When the second transistor 102 is an NFET, the second metaloxide layer 601 may be yttrium oxide (Y₂O₃), lutetium oxide (Lu₂O₃),lanthanum oxide (La₂O₃), strontium oxide (SrO), zirconium oxide (ZrO₂),hafnium oxide (HfO₂), magnesium oxide (MgO), or any combination thereof.

The second metal oxide layer 601 has a thickness in a range from about0.1 to about 2.0 nm. In another aspect, the second metal oxide layer 601has a thickness in a range from about 0.3 to about 0.8 nm.

The third liner layer 602 is disposed as a conformal layer directly ontothe second metal oxide layer 601 within the source/drain trenches 140 ofthe first and second transistors 101, 102. In some embodiments, thethird liner layer 602 may be optional. The third liner layer 602 mayinclude a low contact resistance material or other suitable conductiveliner material. Non-limiting examples of suitable materials for thethird liner layer 602 include titanium nitride, tantalum nitride,tungsten, or any combination thereof. The third liner layer 602 may beformed as a single layer or multi layers of one or more materials.

The third liner layer 602 is formed using any suitable depositionprocess. Non-limiting examples of suitable deposition methods forforming the third liner layer 602 include CVD, PVD, ALD, or anycombination thereof.

The thickness of the third liner layer 602 generally varies and is notintended to be limited. In one aspect, the thickness of the third linerlayer 602 is in a range from about 0.5 nm to about 5.0 nm. In anotheraspect, the thickness of the third liner layer 602 is in a range fromabout 1.0 nm to about 3.0 nm.

FIG. 7 is a cross-sectional side view after disposing a third mask (notshown) over the second transistor 102 and selectively removing thesecond metal oxide layer 601 and third liner layer 602 from the firsttransistor 101. The first metal oxide layer 301 and the second linerlayer 401 remains substantially intact in the first transistor 101. Themask protects the second transistor 102 during etching.

One or more etching processes may be used to selectively remove thethird liner layer 602 and the second metal oxide layer 601 from thefirst transistor 101. A wet etching process that is selective for thethird liner layer 602 material may be employed.

In one embodiment, the third liner layer 602 includes titanium nitride,and an etching process including NH₄OH, H₂O₂, and H₂O (“SC1”) is used toremove the third liner layer 602. A second selective etching process maythen be used to remove the second metal oxide layer 601. In an exemplaryembodiment, a hydrochloric acid etching process is used to remove thesecond metal oxide layer 601.

The mask (not shown) is removed by, for example, an ashing process.After removing the second metal oxide layer 601 and the third linerlayer 602, the first transistor 101 includes the first metal oxide layer301 disposed over the silicon dioxide layer 120. The second liner layer401 is disposed over the first metal oxide layer 301. The secondtransistor 102 includes the second metal oxide layer 601 disposed overthe silicon dioxide layer 120. The third liner layer 602 is disposedover the second metal oxide layer 601.

FIGS. 8A and 8B illustrate a first exemplary embodiment following FIG.7. FIG. 8A is a cross-sectional side view after filling the source/draintrenches 140 of the first and second transistors 101, 102 with a metal803. The metal 803 (material) may be any suitable conductive metal.Non-limiting examples of suitable conductive metals/materials includealuminum, platinum, gold, tungsten, titanium, or any combinationthereof. The 803 metal may be deposited by a deposition process, forexample, CVD, PECVD, PVD, plating, thermal or e-beam evaporation, andsputtering.

One or more additional layers may be disposed between the metal 803 andthe second liner layer 401 within the first transistor 101. One or moreadditional layers may be disposed between the metal 803 and the thirdliner layer 602 of the second transistor 102.

In one embodiment, first layer 801 and second layer 802 are disposedbetween the second liner layer 401 and the metal 803 of the firsttransistor 101. In another embodiment, first layer 801 and second layer802 are disposed between the third liner layer 602 and the metal 803 ofthe second transistor 102. Non-limiting examples of suitable materialsfor first layer 801 include titanium, cobalt, aluminum, zirconium,hafnium, or any combination thereof. One non-limiting examples of asuitable material for second layer 802 includes titanium nitride.

In the first transistor 101, a four-layer contact including first metaloxide layer 301, second liner layer 401, first layer 801, and secondlayer 802 is formed between the silicon dioxide layer 120 and the metal803. In the second transistor, a four-layer contact including secondmetal oxide layer 602, third liner layer 602, first layer 801, andsecond layer 802 is formed between the silicon dioxide layer 120 andmetal 803.

FIG. 8B is a cross-sectional side view after performing a planarizationprocess to polish the surface of the metal 803. The top surface of ILDlayer 110 is exposed. The planarization process may include, forexample, a chemical mechanical planarization (CMP) process.

FIGS. 9A and 9B illustrate a second embodiment following FIG. 7. FIG. 9Ais a cross-sectional side view after removing the second liner layer 401from the first transistor 101 and the third liner layer 602 from thesecond transistor 102 of FIG. 7 before filling the source/drain trenches140 with a metal 803.

One or more additional layers are disposed between the metal 803 and thefirst metal oxide layer 301 within the first transistor 101. One or moreadditional layers are disposed between metal 803 and the second metaloxide layer 601 of the second transistor 102. In one embodiment, firstlayer 801 and second layer 802 are disposed between the first metaloxide layer 301 and the metal 803 within the first transistor 101. Inanother embodiment, first layer 801 and second layer 802 are disposedbetween the second metal oxide layer 601 and the metal 803 of the secondtransistor 102.

In the first transistor 101, a tri-layer contact including first metaloxide layer 301, first layer 801, and second layer 802 is formed betweenthe silicon dioxide layer 120 and the metal 803. In the secondtransistor, a tri-layer contact including second metal oxide layer 602,first layer 801, and second layer 802 is formed between the silicondioxide layer 120 and metal 803.

FIG. 9B is a cross-sectional side view after performing a planarizationprocess to polish the surface of the metal 803. The top surface of ILDlayer 110 is exposed. The planarization process may be, for example, aCMP process.

As described above, various embodiments described herein includesemiconductor devices with two transistors having different source/draincontacts that provide reduced contact resistance. The differentsource/drain contacts in the two transistors are formed simultaneouslyusing a series of protective masks.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, element components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The flow diagrams depicted herein are just one example. There may bemany variations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method of making a semiconductor device, themethod comprising: forming a first source/drain trench over a firstsource/drain region in a first transistor and a second source/draintrench over a second source/drain region in a second transistor; forminga first silicon dioxide layer in the first source/drain trench and asecond silicon dioxide layer in the second source/drain trench; forminga first source/drain contact over the first source/drain region, thefirst source/drain contact comprising a first tri-layer contact disposedbetween the first silicon dioxide layer and a first conductive material;and forming a second source/drain contact over the second source/drainregion, the second source/drain contact comprising a second tri-layercontact disposed between the second silicon dioxide layer and a secondconductive material; wherein the first tri-layer contact comprises afirst metal oxide layer in contact with the first silicon dioxide layer,and the second tri-layer contact comprises a second metal oxide layer incontact with the second silicon dioxide layer.
 2. The method of claim 1,wherein the first metal oxide layer is different than the second metaloxide layer.
 3. The method of claim 1, wherein the first metal oxidelayer is aluminum oxide, and the second metal oxide layer is lanthanumoxide.
 4. The method of claim 1, further comprising disposing aconductive liner layer between the first silicon dioxide layer and thefirst tri-layer contact or the second silicon dioxide layer and thesecond tri-layer contact.
 5. The method of claim 1, wherein theconductive liner layer comprises titanium nitride.
 6. The method ofclaim 1, wherein the first tri-layer contact further comprises a layerof titanium disposed over the first metal oxide layer.
 7. The method ofclaim 6, wherein the first tri-layer contact further comprises a layerof titanium nitride disposed between the layer of titanium and the firstconductive material.
 8. The method of claim 1, wherein the secondtri-layer contact further comprises a layer of titanium disposed overthe second metal oxide layer.
 9. The method of claim 1, wherein thesecond tri-layer contact further comprises a layer of titanium disposedover the second metal oxide layer and a layer of titanium nitridedisposed between the layer of titanium and the second conductivematerial.
 10. A method of making a semiconductor device, the methodcomprising: forming a first source/drain trench over a firstsource/drain region in a first transistor and a second source/draintrench over a second source/drain region in a second transistor; forminga first silicon dioxide layer in the first source/drain trench and asecond silicon dioxide layer in the second source/drain trench;disposing a first metal oxide layer onto the first silicon dioxide layerand along a first sidewall of the first source/drain trench and over thesecond silicon dioxide layer and along a sidewall of the secondsource/drain trench; removing the first metal oxide layer from thesecond source/drain trench; disposing a second metal oxide layerfollowed by a conductive liner layer over the first metal oxide layerwithin the first source/drain trench and directly onto the secondsilicon dioxide layer and along the sidewall of the second source/draintrench; removing by a selective process, the second metal oxide layerand the conductive liner layer from the first source/drain trench; andfilling the first source/drain trench and the second source/drain trenchwith a conductive material.
 11. The method of claim 10, furthercomprising disposing a conductive layer over the first silicon dioxidelayer within the first source/drain trench and removing the conductivelayer from the first source/drain trench before disposing the firstmetal oxide layer.
 12. The method of claim 10, further comprisingdisposing a conductive layer over the second silicon dioxide layerwithin the second source/drain trench before disposing the first metaloxide layer, and then removing the conductive layer along with the firstmetal oxide layer.
 13. The method of claim 10, further comprisingdisposing a titanium layer and a titanium nitride layer between theconductive material and the first metal oxide layer within the firstsource/drain trench and between the conductive material and the secondmetal oxide layer within the second source/drain trench.
 14. The methodof claim 10, further comprising removing the conductive liner layerbefore filling the first source/drain trench and the second source/draintrench with the conductive material.
 15. The method of claim 10, whereinthe first metal oxide layer comprises aluminum oxide, and the secondmetal oxide layer comprises lanthanum oxide.
 16. A method of making asemiconductor device, the method comprising: forming a firstsource/drain trench over a first source/drain in a first transistor anda second source/drain trench over a second source/drain in a secondtransistor; forming a first silicon dioxide layer in the firstsource/drain trench and a second silicon dioxide layer in the secondsource/drain trench, the first silicon dioxide layer directly contactinga top portion of the first source/drain, and the second silicon dioxidelayer directly contacting a top portion of the second source/drain;forming a first source/drain contact over the first source/drain, thefirst source/drain contact comprising a first tri-layer liner disposedbetween the first silicon dioxide layer and a first conductive material,the first tri-layer liner comprising a first metal oxide layer incontact with the first silicon dioxide layer; and forming a secondsource/drain contact over the second source/drain, the secondsource/drain contact comprising a second tri-layer liner disposedbetween the second silicon dioxide layer and a second conductivematerial, the second tri-layer contact comprising a second metal oxidelayer in contact with the second silicon dioxide layer; wherein thefirst metal oxide layer is different than the second metal oxide layer.